Plasma processing apparatus

ABSTRACT

The plasma processing apparatus includes main electrodes  5, 31  opposed to each other with a plasma processing space  15  interposed therebetween. The plasma processing apparatus further has a side electrode  6  opposed to side faces  5 B- 1, 5 B- 2  of the main electrode  5,  as well as a side electrode  32  opposed to side faces  31 B- 1, 31 B- 2  of the main electrode  31.  Therefore, in addition to the plasma processing space  15  between the main electrode  5  and the main electrode  31,  an electric field can be formed in spaces between the side faces of the main electrodes  5, 31  and the side electrodes  6, 32,  the spaces serving as predischarge areas  16 - 1, 16 - 2.  By this electric field, processing gas present in the predischarge areas  16 - 1, 16 - 2  can be transformed into plasma. Electrons and excitation species of the plasma generated in these predischarge areas  16 - 1, 16 - 2  can be supplied directly to the plasma processing space  15.

CROSS-REFERENCE TO RELATED APPLICATIONS

This nonprovisional application claims priority based on Application No.2004-082701 filled on Mar. 22, 2004 in Japan under 35 USC 119(a), theentirety of which is incorporated herein by this reference.

BACKGROUND OF THE INVENTION

The present invention relates to plasma processing apparatuses forperforming such processing as surface reforming, cleaning, machining andfilm deposition with applications of plasma generation and controltechniques. For example, the invention relates to plasma processingapparatuses for use in equipment for manufacturing semiconductors,liquid crystal display devices, EL (electroluminescence) panels, suchflat panel displays as PDPs (plasma display panels), solar cells and thelike.

Conventionally, in manufacturing processes of semiconductors, flat paneldisplays, solar cells and the like, it has been practiced to utilizeplasma generated under reduced pressure to perform such processing asreforming, cleaning, machining and film deposition on a glass substrate(hereinafter, referred to as substrate), a semiconductor wafer(hereinafter, referred to as wafer), or the like.

In recent years, along with heating-up enhancement of cost competitivepower, growing attention has been being focused on atmospheric plasmatechniques that do not require any large-scale equipment such as avacuum chamber or an evacuator. The atmospheric plasma techniques havebeen being put into practice in some processes such as surfacereforming, cleaning and dry etching.

A typical example of the atmospheric plasma techniques is one describedin JP H07-118857 A. This prior art example is explained with referenceto FIG. 13.

FIG. 13 is a schematic sectional view showing an example of the plasmaprocessing apparatus described in above mentioned JP H07-118857 A.

In FIG. 13 are shown a power supply 101, a processing vessel 102, a topsurface 102 a, a bottom surface 102 b, a side face 102 c, an insulator102 d, a porous metal electrode 103, a gas flow passage 103 a, openings103 b, a metal electrode 104, a plasma processing section 105, a firstsolid dielectric 106, a substrate 107, a second solid dielectric 108, agas inlet 109, a gas inlet tube 110, a gas inlet 110 a, a gas outlet 110b, a gas discharge port 111 and a discharge port 112.

In this prior art example, the first solid dielectric 106 is providedall over the metal electrode 104, and the porous metal electrode 103 isprovided opposite the first solid dielectric 106. The porous metalelectrode 103 is enabled to supply reaction gas. Between the first soliddielectric 106 and the porous metal electrode 103 is a space whose sidefaces are covered with the second solid dielectric 108.

In this plasma processing apparatus, the substrate 107 is set within thespace covered with the second solid dielectric 108, and inert gas issupplied to the substrate 107 while reaction gas is supplied to thesubstrate 107 via the porous metal electrode 103. Then, a voltage isgiven to the electrode 103 under a pressure close to atmosphericpressure so that a glow discharge plasma is generated, and activespecies excited by the plasma is put into contact with the surface ofthe substrate 107. Thus, surface processing of the substrate 107 iscarried out.

With regard to the opposing electrode 104 and electrode 103, theelectrode 104 is a metal electrode 104 having the first solid dielectric106 provided on its opposing surface, and the electrode 103 is a porousmetal electrode 103 capable of supplying reaction gas. In thepublication of JP H07-118857 A, it is further described that the porousmetal electrode and the metal electrode are connected so that any one ofthem comes on the anode side and the other is on the cathode side, wherethe two electrodes may be replaced with each other up and down.

Consequently, the following (i) to (vii) are described in JP H07-118857A.

(i) A processing object (substrate 107), which is an article to beprocessed, is placed between opposing electrodes.

(ii) At least one of the opposing electrodes has a solid dielectricprovided on its opposing surface side.

(iii) Reaction gas is supplied to between the opposite electrodes.

(iv) Reaction gas is supplied through the porous metal electrode.

(v) Voltages to be given to the opposite two electrodes are of differentpolarities, but one of them is grounded.

(vi) It is between the opposite two electrodes that the glow dischargeplasma is generated.

(vii) No glow discharge plasma is generated with the porous metalelectrode alone or with the metal electrode alone (plasma is generatedonly with paired electrodes).

However, the above-described prior-art plasma generator has issues shownin (a) to (f) below.

(a) As the distance between the opposing solid dielectric and porousmetal electrode increases, the discharge may be unstable, orlocalization of discharge occurs, or the discharge itself does notoccur.

(b) In a case like (a), increasing the applied voltage for stabilizationof discharge may cause the processing object to be damaged.

(c) The gas use efficiency is low because the decomposition ofprocessing gas less proceeds;

(d) Large-scale equipment is involved; flat-flow processing, i.e.processing the processing object while moving it on a specified plane,is hard to fulfill;

(e) As the distance between the opposing solid dielectric and porousmetal electrode decreases, there occurs processing nonuniformities dueto the opening pattern of the porous metal electrode;

(f) Adjustment of the distance between the opposing solid dielectric andporous metal electrode is hard to do.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to provide a plasmaprocessing apparatus which is capable of generating a stable plasmahaving a wide control range of a working distance under atmosphericpressure and which allows both low running cost and high-speedprocessing to be fulfilled at the same time. Another object of theinvention is to provide a safe, low-priced plasma processing apparatuswhich is free from obstacles to peripheral equipment and human bodies.

In order to achieve the above object, there is provided a plasmaprocessing apparatus comprising:

a gas supply section for supplying a specified processing gas to aplasma processing space where a plasma processing object to be processedis placed;

a first electrode which is opposed to the plasma processing space andwhich generates an electric field in the plasma processing space;

a second electrode which is opposed to the first electrode with theplasma processing space interposed therebetween;

a third electrode which is opposed to a side face of the first electrodewith a specified gap, the side face being adjacent to an opposing faceof the first electrode facing the plasma processing space; and

a first power supply section for supplying a first electric power to thefirst electrode.

In the plasma processing apparatus of this invention, the firstelectrode, to which the first electric power is supplied from the firstpower supply section, forms an electric field against the secondelectrode, by which the electric field is formed in the plasmaprocessing space. Meanwhile, the gas supply section supplies processinggas to the plasma processing space. As a result, the processing gas istransformed into plasma under atmospheric pressure by the electric fieldformed in the plasma processing space. With this plasma-state processinggas, the processing object placed in the plasma processing space isplasma processed.

In this case, an electric field is formed also between the side face ofthe first electrode and the third electrode. By this electric field, theprocessing gas present between the side face of the first electrode andthe third electrode is transformed into plasma. That is, the spacebetween the side face of the first electrode and the third electrodeserves as a predischarge area. When the plasma generated in thispredischarge area reaches a region between the plasma processing spaceand the first electrode, electrons and excitation species are supplieddirectly to the plasma processing space by the plasma. It is noted herethat this phenomenon is referred to as creeping discharge.

As shown above, generating a plasma in the predischarge area causeselectrons or excitation species to be supplied directly to the plasmaprocessing space. When the plasma is not yet generated in the plasmaprocessing space, discharge start in the plasma processing space can beassisted. While discharge is in progress in the plasma processing space,the discharge can be stabilized.

According to this invention, utilization of the creeping dischargeallows the following working effects (I) to (VI) to be expected.

(I) It becomes possible to widen the control range of a working distancebetween the first electrode and the second electrode.

(II) Decomposition of the processing gas is carried out also in thepredischarge area besides the plasma processing space, so that the useefficiency of the processing gas is enhanced.

(III) As compared with conventional plasma generators, plasma can bemaintained even if the electric field in the plasma processing spaceweakened, so that damage to the processing object can be reducedeventually.

(IV) The equipment becomes compact, and flat-flow processing isfacilitated.

(V) The gas supply section is located on the rear face side of the firstelectrode, providing the structure that the processing gas is suppliedto the predischarge area between the first electrode and the thirdelectrode, where the gas jet port of the gas supply section can beseparated from the plasma processing space. Therefore, processingnonuniformities due to the opening pattern of the gas jet port are lesslikely to occur.

(VI) The distance between the first electrode and the second electrodebecomes easier to adjust.

Thus, according to this invention, a plasma which has a wide controlrange of the working distance under atmospheric pressure and which isstable can be generated, making it possible to provide a plasmaprocessing apparatus capable of fulfilling both low running cost andhigh-speed processing.

In one embodiment of the present invention, the plasma processingapparatus further comprises a first dielectric portion with which theopposing face and the side face of the first electrode are covered; and

a second dielectric portion with which a side face of the thirdelectrode opposed to the side face of the first electrode is covered,wherein

the first dielectric portion and the second dielectric portion areopposed to each other with a specified gap therebetween.

In this embodiment, the first dielectric portion, with which theopposing face and side faces of the first electrode are covered, and thesecond dielectric portion, with which the third electrode is covered,are included. Thus, the first electrode and the third electrode can beprevented from being damaged by discharge.

In one embodiment of the present invention, the third electrode isgrounded,

a second power supply section for supplying a second electric power tothe second electrode is provided,

the first electric power supplied to the first electrode by the firstpower supply section and the second electric power supplied to thesecond electrode by the second power supply section are different fromeach other in at least one of phase and amplitude, and wherein

the first electric power and the second electric power are

RF power, or pulse wave electric power, or electric power obtained byswitching RF power and pulse wave electric power, or electric power inwhich RF power and pulse wave electric power are superimposed on eachother.

In this embodiment, the waveform of the first and second electric powermay be selected from among RF power, or pulse wave electric power, orelectric power obtained by switching RF power and pulse wave electricpower, or electric power in which RF power and pulse wave electric powerare superimposed on each other, in consideration of various conditionsrequired for the plasma processing, the type of processing gas, demandedprocessing performance, and moreover electromagnetic interferenceagainst peripheral equipment and safety against the human body. It isnoted here that the RF power refers to electric power having a frequencyof 1 kHz to 100 MHz. The pulse electric power refers to one having arepetition frequency of 1 MHz or lower, a waveform rise time of 100μsec. or less and a pulse application time of 1 msec. or less.

In one embodiment of the present invention, the apparatus has astructure that processing gas supplied by the gas supply section, afterpassing through the gap between the side face of the first electrode andthe third electrode, passes through the plasma processing space betweenthe first electrode and the second electrode.

In this embodiment, the gas supply section is located on the rear faceside of the first electrode, providing the structure that the processinggas is supplied to the predischarge area between the first electrode andthe third electrode, so that the gas jet port of the gas supply sectioncan be separated from the plasma processing space. Therefore, processingnonuniformities due to the opening pattern of the gas jet port are lesslikely to occur.

In one embodiment of the present invention, the gas supply sectioncomprises

a gas jet port for supplying the processing gas to the gap between thefirst electrode and the third electrode; and

an opening controller for changing at least one of opening area andopening configuration of the gas jet port.

In this embodiment, with respect to the gas supply section, by changingthe opening area or opening configuration of the gas jet port by meansof the opening controller, gas flow rate and gas flow velocity can becontrolled. Thus, flow rate and flow velocity of the processing gas tobe supplied to the plasma processing space can be controlled.

In one embodiment of the present invention, the plasma processingapparatus further comprises a dielectric coat formed on the opposingface and the side face of the first electrode, wherein

the first dielectric portion covers the dielectric coat.

This embodiment has a dielectric coat formed on the opposing face andside faces of the first electrode. Therefore, even when the firstdielectric portion is provided as a component independent of the firstelectrode so that the dielectric coat is overlaid with the firstdielectric portion, a gap (space) formed between the first electrode andthe first dielectric portion can be suppressed to a minimum. Thus,reduction of the electric field strength in the plasma processing spaceand the predischarge area can be suppressed, and discharge at the gapcan be suppressed so that occurrence of any power loss and electrodedamage can be suppressed.

In one embodiment of the present invention, the gap between the firstelectrode and the first dielectric portion is not more than 500 μm.

In this embodiment, the gap between the first electrode and the firstdielectric portion is not more than 500 μm. Thus, the effect forsuppressing any reduction of the electric field strength as well as theeffect for suppressing discharge at the gap can be fulfilled. If the gapis over 500 μm, the suppression effects would be insufficient. Inaddition, the gap between the first electrode and the first dielectricportion is more preferably not more than 100 μm.

According to this invention, in addition to the plasma processing spacebetween the first electrode and the second electrode, an electric fieldcan be formed also between the side faces of the first electrode and thethird electrode. By this electric field, processing gas present betweenthe side faces of the first electrode and the third electrode can betransformed into plasma. Therefore, according to this invention, thespaces between the side faces of the first electrode and the thirdelectrode are used as predischarge areas, electrons and excitationspecies of the plasma generated in the predischarge areas can besupplied directly to the plasma processing space.

Consequently, plasma generation in the plasma processing space can beachieved more easily, and besides plasma discharge can be stabilized.Thus, there can be realized a plasma processing apparatus which iscapable of generating a stable plasma having a wide control range of aworking distance under atmospheric pressure and which allows both lowrunning cost and high-speed processing to be fulfilled at the same time.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be more fully understood by the followingdetailed description and the accompanying drawings. However, thedetailed description and the accompanying drawings will be given only byway of illustration and therefore do not limit the present invention.

FIG. 1 is a side sectional view showing a first embodiment of the plasmaprocessing apparatus of the present invention;

FIG. 2 is an enlarged side sectional view showing the construction of amain part of the plasma processing apparatus of the first embodiment;

FIG. 3 is a side sectional view showing the construction of an electrodepart of the plasma processing apparatus of the first embodiment;

FIG. 4 is a schematic sectional view showing another example of theopening control part for controlling the flow rate and flow velocity ofthe gas in the plasma processing apparatus of the first embodiment;

FIG. 5 is a waveform diagram showing an example of the voltage waveformapplied to the main electrode of the plasma processing apparatus of thefirst embodiment;

FIG. 6 is a waveform diagram showing another example of the voltagewaveform applied to the main electrode of the plasma processingapparatus of the first embodiment;

FIG. 7 is a waveform diagram showing still another example of thevoltage waveform applied to the main electrode of the plasma processingapparatus of the first embodiment;

FIG. 8 is a side sectional view showing the construction of a plasmaprocessing apparatus of a second embodiment of the invention;

FIG. 9 is a waveform diagram showing one example of the voltage waveformapplied to the plasma processing apparatus of the second embodiment;

FIG. 10 is a side sectional view showing the construction of a plasmaprocessing apparatus of a third embodiment of the invention;

FIG. 11 is a side sectional view showing the construction of a plasmaprocessing apparatus of a fourth embodiment of the invention;

FIG. 12 is a perspective view of the plasma processing apparatus in thefirst embodiment; and

FIG. 13 is a sectional view of a prior-art plasma processing apparatus.

DETAILED DESCRIPTION OF THE PREFERED EMBODIMENTS

Hereinbelow, the present invention is described in detail by embodimentsthereof illustrated in the accompanying drawings.

First Embodiment

FIG. 1 shows a first embodiment of the plasma processing apparatus ofthe present invention. FIG. 1 is a side sectional view showing a crosssection obtained by cutting the plasma processing apparatus by a planevertical to a plate-shaped processing object 14 and which contains aline segment extending along a direction of conveyance of the processingobject 14. FIG. 2 is an enlarged view showing a main part of the plasmaprocessing apparatus. The processing object 14 is a semiconductorsubstrate as an example.

As shown in FIGS. 1 and 2, this plasma processing apparatus has achamber upper part 1, a chamber lower part 2, an upper electrode unit 3and a lower electrode unit 4. The chamber upper part 1 and the chamberlower part 2 constitute a chamber C. The chamber C has outlet and inlet17 a and 17 b for the processing object 14 at both ends of theconveyance direction between the chamber upper part 1 and the chamberlower part 2.

The upper electrode unit 3 is fitted to an opening formed atapproximately center of the chamber upper part 1 and covered with anupper electrode cover 12. The upper electrode cover 12 has a gas supplyport 21-1 communicating with the upper electrode unit 3.

The lower electrode unit 4 is located at approximately center of thechamber lower part 2 and opposed to the upper electrode unit 3 with aspacing of a specified distance. On both sides of the lower electrodeunit 4 are placed conveyor rollers 13 supported by a roller shaft 23.Conveyor rollers 13 are placed also outside side walls 2 a, 2 b of thechamber lower part 2. These conveyor rollers 13 are enabled to cavitythe processing object 14 along the conveyance direction on a specifiedplane. The chamber lower part 2 has a gas supply port 21-2 communicatingwith the lower electrode unit 4. Further, the chamber lower part 2 hastwo discharge ports 22 penetrating through the chamber lower part onboth sides of the lower electrode unit 4.

As shown in FIG. 3, the upper electrode unit 3 has a main electrode 5 asa first electrode placed at a center portion, and a side electrode 6 asa third electrode having side faces 6B-1, 6B-2 opposed to side faces5B-1, 5B-2 of the main electrode 5. The main electrode 5 and the sideelectrode 6 are made of metal.

The main electrode 5 is covered with a first dielectric portion 7-1 madeof a solid dielectric, and the first dielectric portion 7-1 covers anopposing face 5C, side faces 5B-1, 5B-2 and a rear face 5D of the mainelectrode 5. Also, of the side electrode 6, an end portion 6C includingthe side faces 6B-1, 6B-2 is covered with a second dielectric portion8-1 made of a solid dielectric. The first dielectric portion 7-1 and thesecond dielectric portion 8-1 are opposed to each other with a specifiedgap therebetween, and this gap serves as a predischarge area 16-1.

As shown in FIG. 3, the predischarge area 16-1 communicates with a gasflow passage 26-1 formed in a base portion 6D of the side electrode 6.The first dielectric portion 7-1 is fixed to a portion 6E of the baseportion 6D of the side electrode 6 which portion 6E is adjacent to thegas flow passage 26-1. As shown in FIG. 2, the side electrode 6 has agas storage 9-1 formed of an upwardly-opened recessed portion, and thegas storage 9-1 communicates with the gas flow passage 26-1 and the gassupply port 21-1. The gas storage 9-1, the gas flow passage 26-1 and thegas supply port 21-1 constitute a gas supply section G1. The gas flowpassage 26-1 also forms a gas jet port 11-1 for supplying processing gasto the predischarge area 16-1.

As shown in FIG. 3, in the portion 6E of the base portion 6D of the sideelectrode 6, flow adjusting plates 35-1, 35-1 as opening controllers areplaced so as to be slidable in left-and-right directions. These flowadjusting plates 35-1, 35-1, when slid left and right, causes theopening area and the opening configuration on the inlet side of the gasflow passage 26-1 to be changed.

In the side electrode 6, a through hole 6A is formed, so that arefrigerant 10, when put into flow through the through hole 6A, causesthe side electrode 6 to be cooled. Further, a through hole 5A is formedalso in the main electrode 5, so that the refrigerant 10, when put intoflow through the through hole 5A, causes the main electrode 5 to becooled.

The main electrode 5, which is the first electrode, is connected to anRF (Radio Frequency) power supply 18, which is a first power supplysection, by a power transfer path 27, and the RF power supply 18 isconnected to the ground. The side electrode 6 is grounded by an electricpath 28.

On the other hand, the lower electrode unit 4, as shown in FIG. 3,generally similar in structure to the upper electrode unit 3, has a mainelectrode 31 as a second electrode placed at a center portion, and aside electrode 32 as a third electrode having side faces 32B-1, 32B-2opposed to side faces 31B-1, 31B-2 of the main electrode 31. The mainelectrode 31 and the side electrode 32 are made of metal.

The main electrode 31 is covered with a first dielectric portion 7-2made of a solid dielectric, and the first dielectric portion 7-2 coversan opposing face 31C, side faces 31B-1, 31B-2 and a rear face 31D of themain electrode 31. Also, of the side electrode 32, an end portion 32Cincluding the side faces 32B-1, 32B-2 is covered with a seconddielectric portion 8-2 made of a solid dielectric. The first dielectricportion 7-2 and the second dielectric portion 8-2 are opposed to eachother with a specified gap therebetween, and this gap serves as apredischarge area 16-2.

The predischarge area 16-2 communicates with a gas flow passage 26-2formed in a base portion 32D of the side electrode 32. The firstdielectric portion 7-2 is fixed to a portion 32E of the base portion 32Dof the side electrode 32 which portion 32E is adjacent to the gas flowpassage 26-2. The side electrode 32 has a gas storage 9-2 formed of adownwardly-opened recessed portion, and the gas storage 9-2 communicateswith the gas flow passage 26-2 and the gas supply port 21-2. The gasstorage 9-2, the gas flow passage 26-2 and the gas supply port 21-2constitute a gas supply section G2. The gas flow passage 26-2 also formsa gas jet port 11-2 for supplying processing gas to the predischargearea 16-2.

As shown in FIG. 3, in the portion 32E of the base portion 32D of theside electrode 32, flow adjusting plates 35-2, 35-2 as openingcontrollers are placed so as to be slidable in left-and-rightdirections. These flow adjusting plates 35-2, 35-2, when slid left andright, causes the opening area and the opening configuration on theinlet side of the gas flow passage 26-2 to be changed.

In the side electrode 32, a through hole 32A is formed, so that arefrigerant 10, when put into flow through the through hole 32A, causesthe side electrode 32 to be cooled. Further, a through hole 31A isformed also in the main electrode 31, so that the refrigerant 10, whenput into flow through the through hole 31A, causes the main electrode 31to be cooled.

As shown in FIG. 1, the main electrode 31 is connected to an RF powersupply 33 by a power transfer path 29, and the RF power supply 33 isconnected to the ground. The side electrode 32 is grounded by anelectric path 30.

The distance between the main electrode 5 and the main electrode 31 isset depending on the magnitude and frequency of electric power givenfrom the RF power supply 18, 33, the type and flow rate of processinggas, the electrical characteristics, secondary electron emissioncoefficient and thickness of the solid dielectrics forming thedielectric portions 7-1, 7-2, temperatures of individual parts andsections, and the like.

FIG. 12 shows a perspective view of the plasma processing apparatus ofthe first embodiment. As shown in FIG. 12, a chamber side face member 25is attached to side end faces of the chamber upper part 1 and thechamber lower part 2. A plurality of conveyor rollers 13 are placed alsooutside the chamber lower part 2 so that the plate-shaped processingobject 14 can be conveyed on a specified plane extending through aplasma processing space 15.

In the plasma processing apparatus of the above construction, an RFpower as a first power outputted from the RF power supply 18, which isthe first power supply section, is supplied to the main electrode 5,which is the first electrode, via the power transfer path 27. Also, anRF power as a second power is supplied to the main electrode 31, whichis the second electrode, from the RF power supply 33, which is a secondpower supply section, via a power transfer path 29. As a result, anelectric field is formed between the main electrode 5 and the mainelectrode 31, by which the electric field is formed in the plasmaprocessing space 15. In this embodiment, it is assumed that the RF poweroutputted by the RF power supply 18 and the RF power outputted by the RFpower supply 33 are mutually equal in frequency and different in phase.

On the other hand, a processing gas in which a plurality of gaseousspecies have been mixed by unshown mass flow and mixer is supplied froman unshown gas supply cylinder or gas supply tank to the gas supply port21-1 of the gas supply section G1 of the upper electrode unit 3. Asshown in FIG. 2, the processing gas is supplied from the gas supply port21-1 to the gas storage 9-1, and the gas spreads at this gas storage 9-1in a perpendicular direction to the drawing sheet so as to reach aslit-like (or shower hole-like) gas flow passage 26-1 having across-sectional area sufficiently narrower than the gas storage 9-1. Theprocessing gas is accelerated in flow velocity when passing through thegas flow passage 26-1, passes via the gas jet port 11-1 and thepredischarge area 16-1, and jetted out toward the processing object 14while supplied to the plasma processing space 15. Similarly, theprocessing gas is supplied from the gas supply port 21-2 of the gassupply section G2 of the lower electrode unit 4. This processing gaspasses through the gas storage 9-2, the gas flow passage 26-2, the gasjet port 11-2 and the predischarge area 16-2, thus being supplied to theplasma processing space 15.

In this way, the processing gas introduced from the upper electrode unit3 and the lower electrode unit 4 to the plasma processing space 15 istransformed into plasma under atmospheric pressure by the electric fieldformed in the plasma processing space 15. With this plasma-stateprocessing gas, the processing object 14 conveyed and placed in theplasma processing space 15 is plasma processed. Herein, the term“atmospheric pressure” refers to a pressure range of 0.1 atmosphere to 2atmospheres as an example. The processing gas to be adopted in thisembodiment is given by helium, argon, oxygen, air and the like in thecase of, for example, surface reforming of the processing object 14.However, this processing gas varies in composition from process toprocess, making it necessary to select optimum combination and mixingratio as required.

Then, the processing gas that has passed through the plasma processingspace 15 is temporarily stored in a discharge-side gas storage 20 shownin FIG. 1, passes through the discharge ports 22, being renderedharmless and discharged out of the system by an unshown discharge pumpor blower, in some cases by harm removal equipment.

In this embodiment, an electric field is formed also between the sidefaces 5B-1, 5B-2 of the main electrode 5 and side faces 6B-1, 6B-2 ofthe side electrode 6 in the upper electrode unit 3. By this electricfield, processing gas present between the first dielectric portion 7-1,with which the side faces 5B-1, 5B-2 of the main electrode 5 arecovered, and the second dielectric portion 8-1, with which the sideelectrode 6 is covered, (i.e., present in the predischarge area 16-1) istransformed into plasma. Likewise, in the lower electrode unit 4, anelectric field is formed also between the side faces 31B-1, 31B-2 of themain electrode 31 and the side faces 32B-1, 32B-2 of the side electrode32. By this electric field, processing gas present between the firstdielectric portion 7-2, with which the side faces 31B-1, 31B-2 of themain electrode 31 are covered, and the second dielectric portion 8-2,with which the side electrode 32 is covered, (i.e., present in thepredischarge area 16-2) is transformed into plasma.

In this case, the plasma formation in these predischarge areas 16-1,16-2 is fulfilled by properly selecting the distance between the firstdielectric portion 7-1, 7-2 and the second dielectric portion 8-1, 8-2.This distance depends on the electric power and frequency given to themain electrode 5, 31 by the RF power supply 18, 33, the type and flowrate of the processing gas, the electrical characteristics, secondaryelectron emission coefficient and thickness of the first dielectricportions 7-1, 7-2, 8-1, 8-2, temperature and the like. In thisembodiment, settings are given so that the intensity of the electricfield formed in the predischarge areas 16-1, 16-2 becomes higher thanthat of the electric field formed in the plasma processing space 15.

In this embodiment, the plasma generated in the predischarge areas 16-1,16-2 reaches up to creeping discharge portions 24 of the firstdielectric portions 7-1, 7-2, so that electrons or excitation speciesare supplied directly to the plasma processing space 15 (creepingdischarge). The creeping discharge portions 24 are present between themain electrodes 5, 31 and the plasma processing space 15.

As shown above, generating a plasma in the predischarge areas 16-1, 16-2makes it possible to supply electrons or excitation species directly tothe plasma processing space 15. As a result, when the plasma is not yetgenerated in the plasma processing space 15, discharge start in theplasma processing space 15 can be assisted. While discharge is inprogress in the plasma processing space 15, the discharge can bestabilized. These effects can be further enhanced by eliminating edgesand thereby smoothing the creeping discharge portions 24. As an example,when corner portions of the creeping discharge portions 24 arecurve-shaped, it is desirable that the radius of curvature is set to 0.5mm or more.

Utilization of the creeping discharge allows the following workingeffects (I) to (VI) to be expected.

(I) It becomes possible to widen the control range of a working distancebetween the main electrode 5 and the main electrode 31.

(II) Decomposition of the processing gas is carried out also in thepredischarge areas 16-1, 16-2 besides the plasma processing space 15, sothat the use efficiency of the processing gas is enhanced.

(III) As compared with conventional plasma generators, plasma can bemaintained even if the electric field in the plasma processing space 15is weakened, so that damage to the processing object 14 can be reducedeventually.

(IV) The equipment becomes compact, and flat-flow processing isfacilitated.

(V) The gas supply sections G1, G2 are located on the rear face 5D, 31Dside of the main electrode 5, 31, providing the structure that theprocessing gas is supplied to the predischarge areas 16-1, 16-2 betweenthe main electrode 5, 31 and the side electrode 6, 32, where the gas jetports 11-1, 11-2 of the gas supply sections G1, G2 are separated fromthe plasma processing space 15. Therefore, processing nonuniformitiesdue to the opening pattern of the gas jet ports 11-1, 11-2 are lesslikely to occur.

(VI) The distance between the main electrode 5 and the main electrode 31becomes easier to adjust.

As shown above, in this embodiment, during the generation of plasma bothin the plasma processing space 15 and in the predischarge areas 16-1,16-2, the conveyor rollers 13 are put into rotation to convey theprocessing object 14 so that the surface of the processing object 14comes into contact with the plasma. This allows the plasma processingsuch as surface reforming, cleaning, machining and film deposition toprogress by the reaction acceleration effect of active species and thephysical etching effect of ions, so that desired processing on theprocessing object 14 can be achieved.

Therefore, according to this embodiment, a plasma which has a widecontrol range of the working distance under atmospheric pressure andwhich is stable can be generated, making it possible to provide a plasmaprocessing apparatus capable of fulfilling both low running cost andhigh-speed processing.

In addition, the conveyor rollers 13 are adopted for the conveyance ofthe processing object 14 in this embodiment. However, this is only anexample and a conveyor holder may be used for conveyance. It is alsopossible to perform local plasma processing on the processing objectwithout performing the conveyance during the plasma processing. Further,pulse power supplies 19, 34 may be adopted instead of the RF powersupplies 18, 33.

Also, according to this embodiment, by the provision of the firstdielectric portion 7-1, with which the opposing face 5C and the sidefaces 5B-1, 5B-2 of the main electrode 5 are covered, and the seconddielectric portion 8-1, with which the end portions 6C including theside faces 6B-1, 6B-2 of the side electrode 6 are covered, it becomespossible to prevent the main electrode 5 and the side electrode 6 frombe damaged by discharge. Similarly, by the provision of the firstdielectric portion 7-2, with which the opposing face 31C and the sidefaces 31B-1, 31B-2 of the main electrode 31 are covered, and the seconddielectric portion 8-2, with which the end portions 32C including theside faces 32B-1, 32B-2 of the side electrode 32 are covered, it becomespossible to prevent the main electrode 31 and the side electrode 32 frombeing damaged by discharge.

In this embodiment, as to the gas supply sections G1, G2, it is possibleto change the opening area and opening configuration of the gas jetports 11-1, 11-2 by means of the flow adjusting plates 35-1, 35-2serving as opening controllers, so that gas flow rate and gas flowvelocity can be controlled. Therefore, flow rate and flow velocity ofthe processing gas to be supplied to the plasma processing space 15 canbe controlled.

Also in this embodiment, the main electrodes 5, 31 are covered with thefirst dielectric portions 7-1, 7-2, and the side electrodes 6, 32 arecovered with the second dielectric portions 8-1, 8-2 in the upperelectrode unit 3 and the lower electrode unit 4. These first, seconddielectric portions 7-1, 7-2, 8-1, 8-2 may also be formed directly onthe surfaces of the main electrodes 5, 31 and the side electrodes 6, 32by subjecting the main electrodes 5, 31 and the side electrodes 6, 32 tothermal spraying, anodic oxidation or the like. However, from thestandpoints of manpower and cost in maintenance, the first dielectricportions 7-1, 7-2 and the second dielectric portions 8-1, 8-2 arepreferably made interchangeable as components independent of the mainelectrodes 5, 31 and the side electrodes 6, 32. It is noted that thethickness value of the first dielectric portions 7-1, 7-2 and the seconddielectric portions 8-1, 8-2 is determined in close relation to therepetition frequency of the RF power supplies 18, 33 (or pulse powersupplies 19, 34), the type of the processing gas, and the materialcharacteristics of the dielectric itself. Accordingly, although it isdifficult to commonly determine the value, yet one general example isthat the first dielectric portions 7-1, 7-2 and the second dielectricportions 8-1, 8-2, when given as independent components, are normally 5mm or less thick, preferably. Particularly when the power supplyfrequency becomes above 1 MHz, then the thickness is 2 mm or less, morepreferably.

Further, as the thickness of the first, second dielectric portions 7-1,7-2, 8-1, 8-2 decreases, the electric field strength in the plasmaprocessing space 15 and the predischarge areas 16-1, 16-2 can beincreased while the first, second dielectric portions 7-1, 7-2, 8-1, 8-2are weakened in their strength so as to be more fragile. Because ofthis, their thickness is preferably within a range of 0.5 mm to 5 mm forpractical use. However, when the first, second dielectric portions 7-1,7-2, 8-1, 8-2 are other than independent components, the thickness maybe made smaller than the above range.

Further, in this embodiment, the length in the direction perpendicularto the drawing sheet of FIG. 1 is equal to or more than that of theprocessing object 14. Practically, for this embodiment, it is desirablefor the structure to have a length 20% or more longer than that of theprocessing object 14 in the perpendicular direction to the drawing sheetof FIG. 1.

In this embodiment also, the refrigerant 10 is supplied from an unshownrefrigerant supply unit or refrigerant supply facility, and passesthrough individual parts such as the main electrode 5 and the sideelectrode 6, thereafter being discharged. The refrigerant 10 may also beused for the role of maintaining the temperature of each part of theapparatus without being limited to the purpose of cooling theelectrodes.

Also in this embodiment, the chamber upper part 1 and the chamber lowerpart 2 has an unshown gap adjusting-and-retaining mechanism including amicrometer head or the like so as to be able to hold the upper electrodeunit 3 and the lower electrode unit 4 so that the electrode gap betweenthe main electrode 5 and the main electrode 31 can be set. Besides, thechamber upper part 1 and the chamber lower part 2 serve the role ofstoring the processing gas to block its leakage to the outside until theused processing gas is discharged through the discharge ports 22.

That is, the chamber C is so structured as to be airtight free from gasleakage except the discharge ports 22 and the sites at which theprocessing object 14 comes in and out through the outlet and inlet 17 aand 17 b. Further, depending on the processes and the type of theprocessing gas used, a curtain mechanism or shutter mechanism againstinert gas may be included at the outlet and inlet 17 a and 17 b of theprocessing object 14.

In the sequence of processes of the above plasma processing, it isimportant to stably generate a plasma and to increase the use efficiencyof the processing gas in terms of processing performance and reductionof the running cost. Achieving these involves not only effective gassupply to the plasma processing space 15 but also adjustment of gasdischarge and proper control of the flow rate and flow velocity of theprocessing gas.

For this purpose, there are needs for the mechanism for adjusting thesupply-side conductance (flowability of gas) like flow adjusting plates35-1, 35-2 shown in FIG. 3, and besides for taking balance of gas supplyand discharge in consideration of conductance of the chamber upper part1 and the chamber lower part 2 also at the discharge-side dischargeports 22.

In this case, it is convenient and practical to determine the dimensionsof individual parts based on the following concepts.

More specifically, the effective cross-sectional area of the gas flowpassage is assumed to be S (m²) and the length (distance) of the gasflow passage is assumed to be L (m). Since the gas flow underatmospheric pressure is a viscous flow, the foregoing parameters and theconductance U, which is an index of gas flowability, have a relationexpressed by the following equation (1) on condition that the length inthe perpendicular direction is infinite:U=a·S ² /L  (1)where “a” is a constant which depends on the viscosity coefficient ofgas species and the pressure.

As to the electric power supply, in addition to the RF power supply 18,a pulse power supply 19 or switching of both power supplies or a meansof superimposition of both power supplies may be conceived. The electricpower supply is desirably determined from the viewpoints of variousconditions required for the process such as frequency and repetitionfrequency, the restriction of gas to be used, demanded processingperformance, and the presence or absence of occurrence of any damage.

Herein, as an example, the RF power supply refers to one having afrequency of 1 kHz to 100 MHz, and the pulse power supply refers to onehaving a repetition frequency of 1 MHz or lower, a waveform rise time of100 μsec. or less and a pulse application time of 1 msec. or less.

The flow adjusting plates 35-1, 35-2 shown in FIG. 3 are shown in a casewhere the gas jet ports 11-1, 11-2 are slit-shaped ones, but thoseotherwise may be shower hole-like ones. The upper and lower electrodeunits 3, 4 having the same opening pattern of the gas jet ports 11-1,11-2, but this combination is not limitative and it is needless to saythat all combinations of slit-shaped opening and shower-like opening arepossible.

In addition, instead of the flow adjusting plates 35-1, 35-2 as openingcontrollers shown in FIG. 3, flow adjusting cams 43-1, 43-2 having anelliptical-shaped cross section may be provided at an inlet-side openingof the gas flow passage 26-1 as shown in FIG. 4. Rotating these cams43-1, 43-2 to a specified angle about a central axis allows theinlet-side opening of the gas flow passage 26-1 to be continuouslyvaried in cross-sectional area.

Next, in FIG. 5, an RF voltage waveform 36 given to the main electrode 5by the RF power supply 18 is shown by solid line, and an RF voltagewaveform 37 given to the main electrode 31 by the RF power supply 33 isshown by broken line. In one example shown in FIG. 5, the RF voltagewaveforms 36, 37 are shifted in phase from each other by π. In thiscase, a voltage difference occurring between the main electrode 5 andthe main electrode 31 is a sum (V1+V2) of an amplitude V1 of the RFvoltage waveform 36 and an amplitude V2 of the RF voltage waveform 37.Also, a voltage difference occurring between the main electrode 5 andthe side electrode 6 is V1.

In FIG. 6, one example of the pulse waveform given to the main electrode5 by the pulse power supply 19 is shown by a solid line indicated bynumeral 38, while one example of the pulse waveform given to the mainelectrode 31 by the pulse power supply 34 is shown by a broken lineindicated by numeral 39, in the case where the pulse power supplies 19,34 are provided in place of the RF power supplies 18, 33. In one exampleshown in FIG. 6, the pulse waveforms 38, 39 are shifted in phase fromeach other by π.

Furthermore, in FIG. 7, one example of waveform is shown by a solid lineindicated by numeral 40 in the case where a DC waveform is given to themain electrode 5 by the pulse power supply 19, while one example ofwaveform is shown by a broken line indicated by numeral 41 in the casewhere a DC pulse waveform is given to the main electrode 31 by the pulsepower supply 34.

In each of the examples shown in FIGS. 5 to 7, one example in which thephase difference between the voltage waveform given to the mainelectrode 5 and the voltage waveform given to the main electrode 31 is πhas been shown. However, this phase difference may be other than π.Further, each of the voltage waveforms given to the main electrodes 5,31 may be a waveform formed by switching over an RF waveform and a pulsewaveform, or a waveform in which an RF waveform and a pulse waveform aresuperimposed on each other.

Furthermore, in the upper electrode unit 3 and the lower electrode unit4, the main electrodes 5, 31 are placed in the center while the sideelectrodes 6, 32 are placed on both sides in the above embodiment.However, without being limited to this placement, a side electrode thatis a ground electrode may be placed only on one side of the mainelectrode, or a plurality of side electrodes may be placed on one sideof the main electrode. Further, a plurality of second electrodes may beplaced on both sides of the main electrode.

Second Embodiment

Next, FIG. 8 shows a second embodiment of the plasma processingapparatus of the invention. The second embodiment differs from theforegoing first embodiment in that a lower electrode unit 50 is providedin place of the lower electrode unit 4. The lower electrode unit 50 isconnected to the ground by an electric path 30.

The lower electrode unit 50 has a main electrode 51, and a fore endportion 51A of the main electrode 51 is covered with a dielectricportion 53. The fore end portion 51A has an opposing face 51C opposed toan opposing face 5C of the main electrode 5.

In FIG. 9, one example of RF voltage waveform given to the mainelectrode 5 by the RF power supply 18 is shown by numeral 42. The secondembodiment is similar to the foregoing first embodiment in basicoperations except that the lower electrode unit 50 is grounded. Thissecond embodiment is suitable for cases where a rear face 14A of theprocessing object 14 does not need to be processed, producing advantagesthat the amount of gas used can be saved and the control for powersupply is simplified.

Third Embodiment

Next, FIG. 10 shows a third embodiment of the plasma processingapparatus of the invention. The third embodiment differs from theforegoing first embodiment in that a dielectric spray deposit 61 on asurface of the main electrode 5 and a dielectric spray deposit 62 isformed on a surface of the main electrode 31. The first dielectricportion 7-1 covers the dielectric spray deposit 61, and the firstdielectric portion 7-2 covers a dielectric spray deposit 62.

This third embodiment has the dielectric coat 61 formed on the opposingface 5C and side faces 5B-1, 5B-2 of the main electrode 5. Therefore,even when the first dielectric portion 7-1 is provided as a componentindependent of the main electrode 5 so that the dielectric coat 61 isoverlaid with the first dielectric portion 7-1, a gap (space) formedbetween the main electrode 5 and the first dielectric portion 7-1 can besuppressed to a minimum. Also, the embodiment has the dielectric coat 62formed on the opposing face 31C and side faces 31B-1, 31B-2 of the mainelectrode 31. Therefore, even when the first dielectric portion 7-2 isprovided as a component independent of the main electrode 31 so that thedielectric coat 62 is overlaid with the first dielectric portion 7-2, agap (space) formed between the main electrode 31 and the firstdielectric portion 7-2 can be suppressed to a minimum.

Therefore, according to this embodiment, reduction of the electric fieldstrength in the plasma processing space 15 and the predischarge areas16-1, 16-2 can be suppressed, and discharge at the gap can be suppressedso that occurrence of any power loss and electrode damage can besuppressed. In addition, the gap is preferably 500 μm or less, and morepreferably 100 μm or less.

Fourth Embodiment

Next, FIG. 11 shows a fourth embodiment of the plasma processingapparatus of the invention. The fourth embodiment differs from theforegoing first embodiment in that a chamber D composed of a chamberupper part 71 and a chamber lower part 72 is provided instead of thechamber C composed of the chamber upper part 1 and the chamber lowerpart 2, the chamber D having two upper electrode units 3 and two lowerelectrode units 4. Main electrodes 6, 6 of these two upper electrodeunits 3, 3 are connected to the RF power supply 18 by power transferpaths 27-1, 27-2, respectively, and the main electrodes 6, 6 areconnected to the ground by electric paths 28-1, 28-2, respectively.Also, the main electrodes 31, 31 of the two lower electrode units 4, 4are connected to the RF power supply 33 by the power transfer paths 29,respectively. The side electrodes 32, 32 are connected to the ground bythe electric path 30.

In this fourth embodiment, since a plural pairs of the upper electrodeunit 3 and the lower electrode unit 4 are provided, it becomesimplementable to improve the processing performance when identicalplasma processing is performed in the plasma processing space of eachpair. Further, when different plasma processings are performed in theplasma processing space of each pair, it becomes possible to performsequential processing by the flat-flow method.

The invention being thus described, it will be obvious that theinvention may be varied in many ways. Such variations are not beregarded as a departure from the spirit and scope of the invention, andall such modifications as would be obvious to one skilled in the art areintended to be included within the scope of the following claims.

1. A plasma processing apparatus comprising: a gas supply section forsupplying a specified processing gas to a plasma processing space wherea plasma processing object to be processed is placed; a first electrodewhich is opposed to the plasma processing space and which generates anelectric field in the plasma processing space; a second electrode whichis opposed to the first electrode with the plasma processing spaceinterposed therebetween; a third electrode which is opposed to a sideface of the first electrode with a specified gap, the side face beingadjacent to an opposing face of the first electrode facing the plasmaprocessing space; and a first power supply section for supplying a firstelectric power to the first electrode.
 2. The plasma processingapparatus as claimed in claim 1, further comprising: a first dielectricportion with which the opposing face and the side face of the firstelectrode are covered; and a second dielectric portion with which a sideface of the third electrode opposed to the side face of the firstelectrode is covered, wherein the first dielectric portion and thesecond dielectric portion are opposed to each other with a specified gaptherebetween.
 3. The plasma processing apparatus as claimed in claim 1,wherein the third electrode is grounded, a second power supply sectionfor supplying a second electric power to the second electrode isprovided, the first electric power supplied to the first electrode bythe first power supply section and the second electric power supplied tothe second electrode by the second power supply section are differentfrom each other in at least one of phase and amplitude, and wherein thefirst electric power and the second electric power are RF power, orpulse wave electric power, or electric power obtained by switching RFpower and pulse wave electric power, or electric power in which RF powerand pulse wave electric power are superimposed on each other.
 4. Theplasma processing apparatus as claimed in claim 1, wherein the apparatushas a structure that processing gas supplied by the gas supply section,after passing through the gap between the side face of the firstelectrode and the third electrode, passes through the plasma processingspace between the first electrode and the second electrode.
 5. Theplasma processing apparatus as claimed in claim 1, wherein the gassupply section comprises: a gas jet port for supplying the processinggas to the gap between the first electrode and the third electrode; andan opening controller for changing at least one of opening area andopening configuration of the gas jet port.
 6. The plasma processingapparatus as claimed in claim 2, further comprising a dielectric coatformed on the opposing face and the side face of the first electrode,wherein the first dielectric portion covers the dielectric coat.
 7. Theplasma processing apparatus as claimed in claim 6, wherein the gapbetween the first electrode and the first dielectric portion is not morethan 500 μm.